In recent years, there has been a development in technology that has been applied in the automation of houses, buildings, etc., which has been termed as home automation or domotics.
A key part of home automation is the automation of lighting systems, with devices such as intelligent switches and dimmers, also known as smart switches or dimmers. With the quick development of these technologies, people have begun to adopt smart switches and dimmers for their homes. Smart dimmers allow a user to switch on, turn off, dim a lighting device, control it remotely or measure power consumption.
Smart dimmers usually need three wires to function, that is, a hot or phase wire from the alternating-current (AC) source is connected to one terminal of the smart dimmer, a second wire is connected to another terminal of the smart dimmer and the lighting device to be controlled, and a neutral wire from the AC source is connected to a third terminal of the smart dimmer, which closes the circuit inside the smart dimmer, allowing current flow for the operation of the electronics of the smart dimmer.
Usually, the electrical wiring of homes has only the first two wires in a switch box or wallbox, with the neutral wire absent from the switch box, since common (non-smart) switches or dimmers are connected in series between the AC source and the lighting device. This yields the problem of having to rewire the entire home in order to bring a neutral wire from the AC source to the switch box.
Some smart dimmers measure the power consumption by means of their power supply. Said power consumption is calculated for an entire circuit (one way, line, or gang), i.e. for all the electric loads combined that are connected to the circuit. Therefore, a user cannot measure the power consumption of each individual load. The power consumed by each individual load is useful to know if a lighting device is consuming more power than usual or to know when to replace a lighting device.
A method for power Measurement in a Two-Wire Load Control Device is disclosed in U.S. Pat. No. 9,250,669 B2. More specifically, it is disclosed a load control device for two or three wire switches, that includes a microcontroller and integrated circuits. Wherein the controller detects via a zero-cross detection circuit a zero crossing event. The controller is configured to issue a control signal to a drive circuit to operate the controllably conductive device at a firing time during a half-cycle. The controllably conductive device is implemented as a TRIAC, the TRIAC will become non-conductive when the load current through the TRIAC drops below a rated holding current of the TRIAC at the end of the half-cycle, however, said device relies on an energy storage device (a capacitor), therefore the power is not supplied continuously. Furthermore, the load control device describes a forward phase control and is silent on how to perform reverse phase control, which is more complex and usually requires more electronic components than forward phase control.
A Load Control Device for High-Efficiency Loads in U.S. patent application Ser. Nos. 12/952,920 and 15/131,444 and their families discloses a dimmer switch, for low-power lighting loads, that provides a pure phase-cut waveform. The dimmer switch has implemented a TRIAC, but may alternatively be implemented as one or more silicon-controlled rectifiers (SCRs), or any suitable thyristor. The TRIAC comprises two main terminals that are coupled in series electrical connection between the hot terminal H and the dimmed hot terminal DH, such that the TRIAC is adapted to be coupled in series electrical connection between the AC power source and a LED driver for conducting the load current to the LED driver. The load control device has a mechanical switch that controls the powering of the whole device, and when the mechanical switch is off, the system is unpowered, therefore requiring the physical input from a user to reactivate the load control device. Therefore, the dimmer cannot allow the remote operation of the same if the switch is off, which limits its smart capabilities.
Another dimmer switch for use with lighting circuits having three-way switches is described in U.S. Pat. No. 7,687,940 B2. However, the smart switch can be installed only in three or four-way switches systems, that includes a dimmer switch with a bidirectional semiconductor switch, such as a TRIAC. A controller is coupled to the gate of the TRIAC through a gate drive circuit and controls the conduction time of the TRIAC each half-cycle. A power supply is coupled across the TRIAC and generates a DC voltage VCC to power the controller. A zero-crossing detector determines the zero-crossing points of the AC voltage source and provides this information to the controller. An airgap switch disconnects the dimmer switch and the lighting load from the AC voltage source and therefore de-energizes the controller. A memory is required for storing the present state of the dimmer switch, wherein the lighting control system has implemented a sensing circuit that has a current sense transformer that only operates above a minimum operating frequency, for example, 100 kHz, such that current only flows in the secondary winding when the current waveform through the primary winding has a frequency above the minimum operating frequency, wherein the system includes only two controllably conductive devices or bidirectional semiconductor switches, such as a TRIACs. However, the power supply of the system sometimes is unable to supply power to the controller through the duration of a toggle or switching of the three-way switch, and the controller of the system will reset. Therefore, the reliability of the dimmer is belittled, since a voltage variation will cause a malfunctioning if the power supply does not draw enough energy to keep itself functioning. Additionally, if the state of the power supply or dimmer is not stored in the memory, the power supply will not operate correctly.
A smart dimming solution for LED light bulb and other non-linear power AC loads in U.S. Pat. No. 9,354,643 B2 discloses a dimmer that employs a TRIAC and two IGBTs. The dimmer is capable of switching between at least three distinct modes of operation. In this first mode the current flows solely through TRIAC in both the positive and negative cycles of VAC, while IGBTs remain deactivated. A second mode the current flows solely through one of the IGBTs, depending on the cycle of VAC, while TRIAC remains deactivated. In the third or intermediate mode, TRIAC, both IGBTs are selectively activated and can selectively operate in a forward or reverse phase control embodiment. In this third mode, the majority of current flows to the load through activated TRIAC, but TRIAC can be deactivated before a zero volt crossing by VAC during either the positive or negative cycle. In this mode, TRIAC is deactivated when one of the IGBTs is activated for a very short period of time. An activated IGBT, in essence electrically shorts the TRIAC, which in turn starves TRIAC of the minimal holding current needed to maintain conduction. However, the use of three semiconductor devices complicates the operation and manufacturing, diminishes the reliability due a to a higher number of components for controlling only one lighting load and passively consumes more energy while dimming.
Therefore, it is desired a two-wire smart dimmer power supply that works continuously, does not need a physical input from the user to be activated and deactivated and is able to perform forward and reverse phase control dimming and adapt according to the necessities of the lighting load.